In the diagnosis of thyroid nodules and goiter, we studied 6 patients who developed thyroid nodules, 3 with malignancy, after high dose radiation exposure (greater than 2500 r). Previously, such exposure was thought to cause only thyroid failure. In the treatment of thyroid cancer, serum thyroglobulin (TG) measurement was compared with total body 125I scanning in 49 patients. Screening for residual thyroid tissue or metastases by serum TG requires discontinuation of thyroid hormone replacement. A combination of TG level and 131I scanning is preferable to either test alone. In the syndrome of inappropriate TSH secretion, nuclear T3 binding in firboblasts cultured from 4 patients was examined. No difference from normal was found in the number of affinity of nuclear receptors. In studies on lymphocytic thyroiditis, association with the postpartum state, with Sjogren's syndrome and with systemic lupus erythematosus has been studied. Completion of detailed examinations on 14 patients with Sjogren's syndrome showed that 64% had compensated or frank hypothroidism.